A. Field of the Invention
This invention relates to the field of welding, and particularly to laser welding.
B. Description of the Prior Art
The development of lasers has prompted attempts to use them for welding metals. Lasers provide a clean source of heat which can be precisely focused to follow a weld joint.
A problem with using lasers for welding is the high reflectivity of many metals. If the metal acts as a mirror and reflects a large portion of the beam of light, then little power will be available for making the weld. This is a particularly serious problem for welding metals such as aluminum which have very high coefficients of reflectivity. As shown in Table 1 below, the reflectivity of aluminum is three to four times as high as the reflectivity of type 321 stainless steel.
TABLE 1 ______________________________________ REFLECTIVITY AT 300.degree. K Wavelength of Reflectivity of Reflectivity of light, .mu.m Aluminum 321 stainless steel ______________________________________ 2 .60 .15 4 .75 .20 6 .82 .22 8 .87 .24 10 .89 .25 15 .90 .25 ______________________________________
For metals having high reflectivity such as aluminum, it is very difficult to start the weld and to control the heat input into the weld. Consequently, the laser welding of aluminum has not found substantial commercial application.